Aggregatibacter actinomycetemcomitans

"Aggregatibacter actinomycetemcomitans" is an oral commensal found also in severe infections in the oral cavity, mainly the periodontium. "A. actinomycetemcomitans", previously "Actinobacillus actinomycetemcomitans", is a gram negative facultative non motile rod. It is also associated with non oral infections.

Nomenclature

Recent studies have shown a phylogenetic similarity of "Actinobacillus actinomycetemcomitans" and "Haemophilus aphrophilus", "Haemophilus paraphrophilus", and "Haemophilus segnis" suggesting the new genus "Aggregatibacter" for them [Norskov-Lauritsen N., Kilian M. Int J Syst Evol Microbiol. 2006 Sep;56(Pt 9):2135-46.] .

Importance

It is one of the bacteria which might be implicated in destructive periodontal disease. Although it has been found more frequently in localized aggressive periodontitis, [Slots J. Scand J Dent Res; 1976 Jan;84(1):1-10.] , prevalence in any population is rather high. It has also been isolated from actinomycotic lesions (mixed infection with certain "Actinomyces" species, in particular "Actinomyces israelii"). It possesses certain virulence factors that enable it to invade tissues, such as leukotoxin.

Virulence Factors

- Leukotoxin; kills PMN's and monocytes.

- Cytolethal distending toxin

- Immunosuppression factors that inhibit blastogenesis, antibody production and activate T-suppressor cells

- Inhibition of PMN's functions

- Resistant to complement mediated killing.

"A. actinomycetemcomitans" Serotypes

- a strain, for example ATCC 29523, frequently in oral cavity, variable leukotoxin expression.

- b strain Y4, most frequently in localized aggressive periodontitis, leukotoxin expression.

- c strain ATCC 33384, low leukotoxin.

- serotypes d, e

References